Calibrating the ILS

[mlee]

Hi, could anyone please tell me why you need to calibrate either side of the ILS?
Regards

[ICT_SLB]

To get a better idea of the overall beam structure and to ensure there is no inverted guidance - it could be disastrous if a "Fly Up" glideslope signal was, in fact, a "Fly Down" command from a side lobe caused by interference.

[Basil]

Just looking at my old ILS Operational Flight Check notes which say that (in the seventies) we checked:
GP using theodolite.
Loc range from 30nm 2000ft.
No flags to 25nm.
Emg speech at 15nm.
GP range: No flags to 10nm.
GP slice: No flags to 6deg. No false courses to 9deg.
Loc beam at 5nm. Check width.
Assessment run10nm orbit at 2000ft to check for flags and false courses.
Enrage local ATC by nicking their mushrooms from around the tower :}

[ICT_SLB]

Basil,
Think most Flight Inspection now reconstruct the flightpath from the IRS and correlate the LOC & GS to get the beam rather than use a theodolite. I know it is perfectly possible to obtain the ILS beam quality from a modern FDR as there's sufficient samples of accelerations and LOC & GS to do it.

[Andy Mayes]

Much more efficient these days without the need for the calibrating aircraft to first land to drop off and set up a load of ground equipment they can just start it on their first approach inbound.

Apart from the serial which involves touching down (in reality a touch and go) the aircraft doesn't even need to land (I'm referring to my experience of CAT 1 calibrations) unless to drop off an unsatisfactory certificate to the Tels Engineers!:uhoh:

There used to be only one company around able to do these calibrations, in the UK there are now two that I know of, the newest one uses a PA31 that used to be owned by British Caledonian and looked lovely in their livery.

[Gulfstreamaviator]

Was a very nice 31, I think it was fully two crew configured, and CAA approved for two crew.

I think I flew it at Gatwick for a short while, back in the dark ages.

Glf

[sheppey]

In the Sixties the Australian DCA flying unit based at Melbourne operated two F27 and a DC3 on flight calibration work around Australia, The British Solomon Islands and New Guinea.
The ILS test included flying inbound at various combinations of full scale fly-up/down and full scale yellow/ blue edges from the outer marker. The old fashioned OBS indication was used by tech crew down the back of the cabin to bias the pilots OBS indicator ILS needles so that from the pilots viewpoint it displayed "correct" tracking - in other words, needles centred.

Naturally we flew VMC with the pilots heads down raw data to 200 ft (no FD in those days) during the checking of the fly up signals and coming in very low at 1.9 degrees and full scale localiser. The pilots OBS was biased to show on course since if the pilot looked outside it was easy to become disorientated at such unusual visual angles.

That experience over the several years I was in the job gave one great personal satisfaction at pure instrument flying skill, particularly as we often flew 20 approaches in an hour from all sides - all raw data.

The sheer love of the challenge of flying raw data meant I could never understand during my latter career as an airline pilot on the 737, why airline pilots shied away from the opportunities that always presented themslves during line flying, to keep in practice at raw data ILS.

Instead, over the years until retirement I observed on a daily basis the increasing trend of almost blind reliance by airline pilots, on the flight director. This eventually led to the children of the magenta line syndrome discussed many times in Pprune pages.